The present invention relates to the field of mass storage devices. More particularly, this invention relates to a method and apparatus for depositing a lubrication layer on a storage disc using a vapor deposition technique.
One key component of any computer system is a device to store data. Computer systems have many different places where data can be stored. One common place for storing massive amounts of data in a computer system is on a disc drive. The most basic parts of a disc drive are an information storage disc that is rotated, an actuator that moves a transducer to various locations over the disc, and electrical circuitry that is used to write and read data to and from the disc. The disc drive also includes circuitry for encoding data so that it can be successfully retrieved and written to the disc surface. A microprocessor controls most of the operations of the disc drive as well as passing the data back to the requesting computer and taking data from a requesting computer for storing to the disc.
The transducer is typically placed on a small ceramic block, also referred to as a slider, that is aerodynamically designed so that it flies over the disc. The slider is passed over the disc in a transducing relationship with the disc. Most sliders have an air-bearing surface (ABS) which includes rails and a cavity between the rails. When the disc rotates (generally, at rotational speeds of 10,000 RPM or higher), air is dragged between the rails and the disc surface causing pressure, which forces the head away from the disc. At the same time, the air rushing past the cavity or depression in the air-bearing surface produces a negative pressure area. The negative pressure or suction counteracts the pressure produced at the rails. The slider is also attached to a load spring, which produces a force on the slider directed toward the disc surface. The various forces on the slider equilibrate, so that the slider flies over the surface of the disc at a particular desired fly height. The fly height is the distance between the disc surface and the transducing head, which is typically the thickness of the air lubrication film. This film eliminates the friction and resulting wear that could occur if the transducing head and disc were in mechanical contact during disc rotation. The layer of lubricant substantially prevents loss of magnetic material (and the data stored therein) and minimizes friction between the head and the disc. In some disc drives, the slider passes through a layer of lubricant rather than flying over the surface of the disc. For recording and reading reliability, it is essential that the thickness of the layer of lubricant be very small so as to not to increase substantially the distance between the head and the magnetic material. It is also essential that the thickness of the coating of the lubricant be very uniform.
In the disc drive industry, high-performance, thin-film storage discs produced by depositing successive layers on a substrate apparatus for preparation of such storage discs are well known in the art. For storage discs of the type formed on a rigid disc substrate, each layer in the storage disc is deposited in a separate chamber. For example, the under-layer, the magnetic layer, and the over-layer (lubrication layer) are generally deposited in separate processing chambers. The lubrication layer can be deposited using a sequential dip coating or a vapor deposition technique (vapor lubrication process).
Application of the lubricant layer to the disc surface is generally the final step in the manufacturing of storage discs, after the discs have been coated with magnetic material. Generally, the magnetic material is deposited onto the disc surface using a sputtering process. The main or common transport chamber including the process chambers are all generally held under low working pressure, e.g., typically around 5xc3x9710xe2x88x925 to 5xc3x9710xe2x88x929 Torr, by means of high performance vacuum pumps. Generally, the process chambers are positioned along the main chamber and receive substrates for sequential processing.
The method and apparatus for the vapor lubrication process includes evaporating lubrication molecules continuously in a vapor lubrication station held under vacuum using a specially designed evaporator, and emitting evaporated lubrication molecules through special diffuser plates to control vapor emission onto the discs to provide a uniform thickness of lubricant on the disc surface. One problem with the vapor lubricating apparatus is cross-contamination of the lubrication molecules that are not deposited on the disc surface that can migrate either by vapor transport or surface migration into adjacent process chambers, such as sputtering chambers and hence can contaminate the adjacent process chambers. For example, after deposition of a carbon overcoat onto a disc substrate using sputtering and removal of the substrate from the carbon-overcoat processing chamber for transfer to a vapor lubrication processing chamber downstream, lubrication molecules that are not deposited on the disc surface in the vapor lubrication station can migrate into the sputtering chamber. The same type of cross-contamination can occur when transferring the disc from the vapor lubrication process to other downstream or upstream processes. Cross-contamination of lubrication molecules is generally undesirable, since it can affect the properties of the medium. Another problem encountered with such cross-contamination is buildup of lubrication molecules within the adjacent process chambers such as the sputtering chamber. This lubrication molecule buildup must be removed from these chambers. Removal of the lubrication molecule necessitates a shutdown of the apparatus, reducing productivity.
What is needed is an improvement to the current method and apparatus of vapor lubrication process that can significantly reduce cross-contamination of lubrication molecules in the upstream and downstream process chambers.
A method for preventing migration of lubrication molecules into adjacent process chambers while coating a thin layer of lubricant over a storage surface of a disc using a vapor lubrication process. Further, the method reduces cross-contamination in upstream and/or downstream process chambers during transfer of the storage discs between the upstream, downstream, and vapor lubrication process chambers. The method includes trapping the lubrication molecules that are not deposited onto the storage surface of the discs during the vapor lubrication process in a vapor lubrication station by using one or more cold traps including cold trapping surfaces. The method can further include sensing the temperature of the cold trapping surfaces and shutting down the vapor lubrication station to prevent accidental migration of lubrication molecules into the adjacent process chambers due to a failure in the operation of the cold traps.
Also discussed is a vapor lubrication station that includes one or more cold traps to prevent migration of lubrication molecules that are not deposited onto storage discs during a vapor lubrication process in the vapor lubrication station into adjacent process chambers. Further, the cold traps include cold trapping surfaces to trap and prevent migration of lubrication molecules into transport chambers used in transporting the storage discs between the process chambers. Also, the station includes one or more temperature sensors to sense the temperature of the cold trapping surfaces and to output a signal proportional to the temperature. Further, the station includes control circuitry coupled to the temperature sensors to automatically shut-off the operation of the vapor lubrication station to prevent accidental migration of lubrication molecules in case of a failure in the operation of the cold traps.
Advantageously, the method and apparatus described above provides cold traps that can significantly reduce cross-contamination in upstream and downstream process chambers and/or during transfer of the storage discs between downstream, upstream, and vapor lubrication process chambers.